1. Field of the Invention
This invention relates generally to a dialysate filter which is easy to install, durable and cost effective. In particular, the invention relates to a dialysate filter which removes bacteria and endotoxins from a dialysate stream before it enters an artificial kidney. Still further, the dialysate filter of the present invention includes improved asymmetrical, microporous, hollow fibers incorporating a polyimide.
2. Description of the Related Art
A dialysate filter is a device which can be used in-line, between a dialysis apparatus and an artificial kidney (dialyzer) during hemodialysis treatments, to remove bacteria and endotoxins from the dialysate stream. Endotoxins are potentially lethal lipopolysaccharide (LPS) molecules which are released when gram-negative bacteria disintegrate or are destroyed.
Endotoxins can cause Pyrogenic Reactions (PRs) in dialysis patients either directly by passing through an artificial kidney membrane into the patient's bloodstream, or indirectly, by inducing a reaction across the artificial kidney membrane. PR(s) are one or more symptoms caused by exposure to endotoxins during dialysis, including fever, chills, hypotension, headache, myalgia, nausea and vomiting. Symptoms usually begin within 30-60 minutes after dialysis has begun, and, vanish shortly after dialysis is stopped. Indirect PR(s) may occur when endotoxins, while remaining trapped within the membrane, still influence changes in a dialysis patient's bloodstream without actually physically contacting the blood.
The role of endotoxins in the long-term morbidity and mortality of dialysis patients is unclear; however, we do know that endotoxins have the ability to stimulate monocytes to produce chemicals called cytokines. These cytokines induce fever and catabolism in dialysis patients. The present invention is a means for preventing PR's by using sterile, non-pyrogenic dialysate during dialysis treatment.
The prior art has promoted a number of alternatives for removing endotoxins from dialysate. These alternatives include an artificial kidney, ultrafiltration apparatuses, hemo-filters and in-line water filters. These alternatives suffer from a number of disadvantages including difficulty in use, expense and safety risks.
One significant safety risk of these modified devices is in the event of a fiber rupture, the filter can release enormous quantities of accumulated endotoxins into the dialysate stream. This may present too large a challenge for the dialyzer to overcome and the dialysis patient may suffer unpleasant consequences as a result. Also, if a portion of this assumed-to-be sterile dialysate solution is diverted and re-infused into the extracorporeal blood circuit, as may be done in hemodiafiltration, then bacteria and endotoxins may be injected directly into the patient's bloodstream.
Previous studies have made claims to endotoxin free dialysate. These claims may be not be completely accurate. Certain smaller endotoxin fragments may be Limulus Amebocyte Lysate assay (LAL) non-reactive. This means that much of the research done which has used LAL to measure passage of endotoxins through dialyzer membranes may be inaccurate. In other words, studies which claimed that no endotoxin passes through dialyzer membranes and used LAL to validate that claim may be inaccurate.
Also, there is some indication that certain smaller endotoxin fragments may pass through conventional dialyzer membranes when they may not pass through high flux membranes. This may be due to differing membrane properties such as mechanisms of adsorption, tortuous pathways, and ionic repulsion. In view of this endotoxins are not merely a concern for high flux dialysis, but for conventional and high efficiency dialysis also.